The correction of heart valve defects, such as valvular insufficiency, may be accomplished through various surgical interventions, including surgical replacement of the entire valve, repairing the valve leaflets, shortening or replacing the chordae tendinae or repairing the valve annulus. Although prosthetic devices are often used to replace dysfunctional or diseased valves, this approach is quite traumatic to the patient and requires lengthy and difficult surgical procedures. Hence, the preferred method of treating such valves is to perform, if possible, more conservative surgical procedures that address the problem yet preserve the patient's native valve.
A variety of such procedures have been developed to correct heart valve defects without resorting to a full valve replacement. An example of such a procedure is that which was developed by Dr. Norberto G. De Vega in the early 1970s. Dr. De Vega's procedure involves creating one or more seams within the tissue along the periphery of a weakened section of heart valve using conventional suture material. The suture is laced through the tissue along the periphery of the valve and the ends of the suture are pulled together in a "purse string" manner to constrict the annulus of the valve so that the valve is patent. The ends of the suture are then tied in place to retain the tissue in a plicated orientation.
Dr. De Vega's procedure offered many advantages for the cardiac surgeon and the patient. In particular, the procedure is sufficiently safe since it introduces a limited amount of foreign material with blood exposure within the heart thereby reducing the risk of thrombosis and is relatively effective at correcting valvular insufficiency. In addition, the procedure required little specialized equipment and could be rapidly performed with minimal training.
However, there were also serious drawbacks associated with Dr. De Vega's technique. For example, there have been several instances whereby the suture that is laced through the tissue along the periphery of the valve pulls out of the tissue. As a result, the suture tends to "guitar string" across the valve annulus forming an obstruction across the valve opening. Another problem is the bunching of tissue around the periphery of the valve caused by the "purse string" design. The bunched tissue causes the valve opening to distort from its natural shape thereby impeding proper valve function.
Another procedure was developed that addressed many of the problems associated with Dr. De Vega's technique. Dr. Alain Carpentier designed a series of multi-sized fabric covered rings with a stainless steel or titanium core. The rings are configured to approximate the original shape of the diseased or dysfunctional valve annulus. Dr. Carpentier's procedure involves sizing the annulus of the valve using a sizing template and selecting a corresponding fabric covered ring. A number of sutures are sewn around the periphery of the annulus creating a circle of guide lines. The ring is positioned on the valve annulus and the guide lines are then attached to the ring, thereby drawing the valve opening to the configuration of the ring and the approximate shape of the original valve annulus. Although Dr. Carpentier's method significantly improves valve function, some surgeons believe that the rigid rings somewhat compromise the natural flexibility of the valve due to the ring's rigid structure.
In response, rings having greater flexibility have also been introduced. Such flexible rings avoid constraining the natural flexibility of the annulus, yet still assist greatly in improving valve function. There are some disadvantages with flexible rings as well. For example, when the suture spacing on the annulus is not matched to the spacing on the ring, tension may result in the tissue and the device, further causing puckering in the tissue. Another example involves the loss of annulus flexibility over time. Since the flexible ring is secured to the valve annulus with a large number of sutures, scarring and stiffening of the valve annulus may develop. This results in a valve physiology similar to what may result when a rigid ring is installed, whereby the natural flexibility of the valve may be somewhat compromised.
A more recent flexible ring design has been proposed in U.S. Pat. No. 5,450,860 to address some of the aforesaid drawbacks. The flexible ring design in this patent includes an open ring in the form of a wide, flexible ligament that is implanted into the valve annulus. The ligament is typically made of expanded polytetrafluoroethylene to give the ligament its flexibility, promote tissue ingrowth and allow sutures to readily pass through it. Although this design substantially removes the ring from the blood flow in the valve, it has some inherent shortcomings.
For example, the material characteristics of the ligament have a tendency to cause the ligament to elongate or stretch when subjected to loading during implantation of the device in the annulus and once the heart is re-started. As a result, the valve structure and function may be compromised. In addition, this ligament design does not ensure the prevention of sutures tearing through the material when the ligament is anchored to the tissue. Therefore, there is a potential risk that the sutures will tear through the ligament, either during the implantation procedure or after the ligament has been implanted in the valve annulus, thereby resulting in valve insufficiency.
In view of the foregoing, it is apparent that a number of surgical procedures have been developed that avoid the dramatic step of replacing a native heart valve yet still assist in restoring normal valve function. It is also apparent, however, that these more conservative procedures still require improvement, particularly as it relates to the drawbacks associated with use of a flexible annuloplasty device. In particular, it is apparent that there is a continuing need to provide an annuloplasty system with a more durable prosthesis that minimizes blood exposure and is also safe and effective to use. There is also a need to provide a method of implanting such an improved prosthesis that requires a limited amount of specialized equipment, has a fast learning curve and can be performed in a minimal amount of time.